Heat sensitive recording papers form a record of images by taking advantage of a physical or a chemical change of matter caused by application of thermal energy thereto, and a great many processes therefor have been studied.
As for a process of utilizing a physical change caused in a substance by applied heat, the so-called wax type of heat sensitive paper has long been known, and particularly has been used for recording electrocardiograms or the like. On the other hand, various kinds of coloring mechanisms through which images can be recorded have been proposed as processes of utilizing a chemical change caused by heat, with the so-called two-component coloring type of heat sensitive recording paper being especially representative thereof.
In the two-component coloring type of heat sensitive recording paper, a record can be obtained by taking advantage of a color reaction which takes place under such circumstances that two kinds of thermally reactive compounds which are dispersed as fine particles isolated from each other by the binder or the like are coated on a support and thereto, heat is applied to melt either or both of the compounds, which thereby come into contact with each other. In general, such two kinds of thermally reactive compounds are a so-called electron-donating compound and a so-called electron-accepting compound.
The two-component coloring type of heat sensitive recording paper as described above has many advantages, in that: (1) the color reaction obeys a first-order kinetics and therefore, no developing step is required; (2) the quality of the recording paper is akin to that of plain paper; (3) the recording paper can be handled with ease; and so on. When colorless dyes are used as the electron-donating compound, the recording paper has further advantages, in that: (4) color density is high; and (5) a wide variety of hues can be easily obtained by the color reaction, which further enhances the utility value of the recording paper of such kind. Accordingly, it has been most frequently employed as a heat sensitive recording material.
In recent years, heat sensitive recording papers have been in increasing demand, particularly in the arts of facsimile transmission equipment, recorders, and printers.
On the other hand, recent advances in integration techniques has increased the tendency toward miniaturizing recorders installed in facsimile transmission equipment, printers, etc., in spite of providing it with many functions.
Integration and miniatuarization of recorders have posed a new problem that mis-operation and production problems are caused by static electricity generated in a recording system including the recorder and the recording paper.
As a measure to counter such troubles, it has generally been carried out to suppress generation of static electricity by imparting electrical conductivity to a heat sensitive recording paper.
A conventionally known method for imparting electrical conductivity to a heat sensitive paper involves addition of a conductive compound, such as a water-soluble inorganic salt, a metal or a metal oxide, a cationic surface active agent such as a quaternary ammonium salt, a nonionic surface active agent like polyethylene glycol, polypropylene glycol, etc., or an anionic surface active agent like a sulfonate (as described in Japanese Patent Application (OPI) Nos. 148687/82, 156292/82 and 170794/82 (the term "OPI" as used herein refers to a "published unexamined Japanese patent application")).
However, those conductive compounds suffer from defects that they do not always have a sufficient conductivity effect to prevent static electricity from being generated in a heat sensitive paper; or, if they do produce a sufficient conductivity effect, they may have an adverse effect on coating facility due to increasing the viscosity of the coating composition or a condensation phenomenon which are caused by addition thereof, and so on. Therefore, these conventional methods have not been completed satisfactory.